In central air conditioning systems typically used in residences, a compressor is operable to circulate a vapor compression refrigerant between an indoor heat exchanger and an outdoor heat exchanger. In recent years, scroll-type compressors for the most part have replaced reciprocating-type compressors in residential air conditioning systems. For cost reasons, such scroll-type compressors typically do not include vibration-dampening springs to isolate the motor and compressor mechanism from the outer housing of the compressor. The refrigerant lines on the suction and discharge sides of the compressor are rigidly attached to this outer housing. Therefore, there is a direct vibration transmission path from the motor and compressor to these refrigerant lines.
In particular the refrigerant line between the indoor heat exchanger and the compressor is susceptible to such vibrations because the line is relatively rigid due its relatively large diameter (e.g., ⅞ inch). In a non-heat pump air conditioning system, where the indoor heat exchanger operates as an evaporator, this refrigerant line corresponds to the compressor suction line, through which vapor refrigerant is drawn from the evaporator to the compressor. The length of this suction line may be about 40 feet, with most of the line being inside the building that is serviced by the air conditioning system. In a heat pump system, this refrigerant line corresponds to the compressor suction line when the system is operated in a cooling mode and to the compressor discharge line when the system is operated in a heating mode.
Such vibrations in the refrigerant line between the compressor and indoor heat exchanger may cause a droning noise that is readily detectable by occupants of the building. This droning noise results when a vibration typically associated with electric motor noise (e.g., approximately 60 Hz and/or one or more harmonic frequencies thereof) is modulated by a low frequency (2 Hz or less) standing wave in the refrigerant line, which varies the intensity of the vibration. The standing wave causes displacement of the refrigerant line, such that contact between the line and a wall, floor or other structural component results in points of noise transmission inside the building.
One solution that has been proposed to inhibit such vibrations is to strap one or more strips of rubber around the refrigerant line, which reduces vibration by adding mass to the line and by frictional damping. This solution typically is used as a “field fix” after the system installer has received a complaint about noise from a customer. The number of rubber strips needed is determined in the field, largely by trial and error.